The importance of nonwoven fabrics in computer diskettes is now recognized as being more than a protective fabric to minimize wear or abrasion of the magnetic media. The wiping action of the fabric is important to the function of the floppy disk medium which stores information for use in a disk drive. The wiping action of the fabric is also important because debris that may interfere with information transfer at the read-write head of the computer disk drive is ideally removed and entrapped by a wiping fabric. Keeping the magnetic disk clean reduces errors in the transmission of information onto or from the magnetic disk.
Computer diskette cartridges are generally designed to provide a substantially closed and dust free environment for the disk. However, contaminants can infiltrate the disk through the hub or read/write window of the cartridges. Debris originates from many sources such as the diskette manufacturing process, the cartridge itself, the action of the read-write head on the magnetic disk, the external environment, and abrasion of the magnetic disk.
Thus, it is desirable to provide liner fabrics having high cleaning and low debris characteristics, which do not abrade the magnetic surface of the disk. For this purpose, it is desirable to engineer fabrics that include fibers that do not produce debris during fabric manufacture and application. If debris created by abrasion is not removed, or if the wiping fabric abrades the magnetic disk producing foreign particles, then the foreign particles may get between the read/write head and the magnetic media, causing a loss of signal strength due to separation. Such separation of the read/write head from the media causes errors in information that is being transferred from or onto a magnetic disk, and a misreading of said information would take place.
Many attempts have been made in the prior art to provide a diskette liner that produces a minimal amount of debris without impinging on the liner's cleaning ability. To improve cleaning ability, cellulosic fibers such as rayon are generally used in diskette liners. The superior performance of a cellulosic containing diskette liner has been demonstrated by the overwhelming preference for these products in the marketplace, particularly with the more demanding 3.5" cartridges which contain higher bit density flexible magnetic media. For example, U.S. Pat. No. 5,122,919 to Takemae discloses a diskette liner made of a mixture of cellulosic fiber (particularly rayon) and a polyester, core-sheath type conjugated fiber. U.S. Pat. No. 5,179,487 to Niitsuma discloses a three-layered diskette liner having both outer layers made of a mixture of rayon and polyester fiber and the inner layer made of acrylic fibers.
However, cellulosic fibers are also known to have the tendency to break apart when cut, which causes fiber debris. Further, cellulosic fibers are absorbent. Therefore, any moisture in the disk environment results in the lengthening of the cellulosic fibers (i.e. longitudinal extension) and destabilization of the liner structure. When the fibers dry, a puckering effect in the liner fabric may also result.
U.S. Pat. Nos. 4,803,584, 4,897,752 and 5,029,319, all to Doi, show other methods for reducing debris in and strengthening thermally bonded liners. The Doi '584 and '752 patents each disclose a three-layered diskette liner in which the media-contacting layer is made of acrylic fibers, which may be mixed with up to 50% of other fibers including rayon. These references generally provide additional thermal bonding in or around the liner or use stiffener layers or anti-dust layers or materials. The additional layers, dust prevention and strengthening procedures tend to make the manufacturing process more costly and complicated. Further, these liners generally have low strength and stiffness characteristics and a high level of debris. Significant amounts of free fiber pieces and other debris also result from cutting and processing the liner fabric during diskette manufacturing.
U.S. Pat. Nos. 4,586,606 and 4,610,352 to Howey, assigned to International Paper Company, the assignee herein, disclose computer diskette liner materials which comprise an inner layer of substantially low melting point thermoplastic material, and at least one outer layer of substantially non-thermoplastic textile length fibers. Preferably, the non-thermoplastic fibers are rayon fibers and the liners comprise one inner layer and two outer layers to form a symmetrical structure. In the '606 patent, rayon comprises 60-100% of each of the two outer layers and 0-50% of the inner layer, thereby making a composite liner comprising 40-85% rayon fibers. The '352 patent discloses a liner comprising 85% rayon. The inner and outer layers of each liner are thermally bonded together at several discrete bonding points by heat and pressure or other similar bonding methods. During the bonding process the low melting thermoplastic materials of the inner layer melt and bond the non-thermoplastic fibers together at discrete bond points which may be recessed beneath or below the outer surface of the fabric. The non-thermoplastic fibers in the bonded laminate do not melt and maintain their original physical properties. Accordingly, a diskette liner is provided including an outer textile surface for use in wiping a magnetic media which is lofty and soft. The Howey diskette liners are further characterized by low levels of debris, high compressibility, low abrasiveness, good dimensional stability and low surface resistivity, which are all features desired for wiping materials for cleaning magnetic media.
Therefore, multi-layered computer diskette liners are known in which one or more outer layers (A) contain rayon fibers or a combination of fibers including rayon, and an intermediate layer (B) contains binder fibers to bond the outer layers together. Typically, these composite liners have a symmetrical structure (i.e., A-B-A or A-B) and can be used with either of the rayon containing outer layers (A) as the media contacting side.
It has now been found that an improved diskette liner can be made by having at least three distinct layers (A-B-C) wherein the composite liner's cellulosic content is substantially reduced and the low-melt thermoplastic binder fibers (i.e., in the B layer) are isolated from the distinct outer layers (A and C). In particular, thermally bonded liners having a reduced cellulosic content are found to have reduced levels of debris, improved hygroscopic dimensional stability and smooth cut edges.
Accordingly, it is a broad object of the invention to provide a computer diskette liner that has improved cleaning ability.
A more specific object of the invention is to provide a computer diskette liner that is substantially free of debris.
Another object of the invention is to provide a computer diskette liner having a reduced cellulosic content and smooth cut edges.
A still further object of the invention is to provide a computer diskette liner that provides improved hygroscopic dimensional stability.